The basal ganglia constitute one of the most ancient and stable features of the vertebrate telencephalon. Dysfunction of the basal ganglia has been related to diverse ailments including Parkinsonism, Huntington's chorea, athetosis, hemiballismus, chronic alcoholism and drug addiction. The proposed research program has as its key objective the continuation of a series of experiments aimed at applying the comparative approach to the study of the role of the basal ganglia in the neural control of behavior. Recent research has indicated that the basal exert control over the optic tectum in both mammals and avian forms. In mammals these pathways are related to the subthalamus and substantia nigra. In avian forms these pathways are related to a complicated series of connections between the paleostriatal complex of the telencephalon and the thalamus. The significance of these neural pathways may be to provide channels by which the basal ganglia can modify attentional and orientation behaviors. The proposed series of experiments represent a continuation of studies designed to elucidate the nature of these connections. Anatomic experiments are based on the use of horseradish peroxidase, a retrograde transport marker. This' histochemical procedure will be used to map the connections of the paleostriatal complex with the thalamus and other parts of the telencephalon, in order to gain an understanding of the role of the basal ganglia in the neural control of vertebrate behavior.